1. FIELD OF THE INVENTION
This invention relates to a method for producing powder metal dies such as for use in the compacting of permanent magnet alloy powders to produce therefrom fully dense, consolidated articles.
2. DESCRIPTION OF THE PRIOR ART
It is known to produce permanent magnets from permanent magnet alloys that are consolidated in powder form into substantially fully dense articles. Permanent magnet alloys of this type include barium and strontium ferrite, as well as alloys including rare earth elements in combination with transition elements.
In powder metallurgy operations and particularly the production of magnets the alloy is produced in particle form of usually less than 100 microns. These powder particles are pressed in mechanical or hydraulic presses using die presses well known in the powder metallurgy industry.
In magnet production practices of this type, it is common to orient the powder particles while in the die of the die pressing apparatus by the use of a magnetic field to cause the particles to align with their best magnetic crystallographic direction parallel to the applied magnetic field. Magnets having this alignment are commonly termed anisotropic magnets.
In the production of anisotropic magnets, and particularly during the magnetic alignment operation, the die in which the magnet alloy particles are contained for alignment and die pressing must be nonmagnetic. Otherwise, the magnetic flux would be short-circuited through the die to result in insufficient alignment or misalignment of the particles within the die.
Since magnet alloy particles of these compositions are extremely abrasive, during the die pressing operation the die cavity is subjected to high wear conditions. Consequently, it is typical to produce dies for this application of nonmagnetic, wear resistant alloys, such as austenitic stainless steels, bronze and brass alloys and nickel base alloys. These alloys are typically cast or forged to form a die block with the required die cavity being formed therein by machining and polishing operations. To enhance wear resistance the die cavity is clad or lined with a carbide, typically tungsten or molybdenum carbides. Alternately, the die cavity may be hardened by surface nitriding or applying a hard facing alloy by welding, flame spraying or vacuum deposition.
Conventional dies produced by the aforementioned practices are not only costly but the wear resistant cladding or surface hardening of the die cavity gives rise to premature failure by cracking or chipping because of the brittle nature of these die cavity surface portions.